Apparatus and methods for automatically inspecting and analyzing images of patterned articles by comparing the images to a computer generated reference, are well known in the art.
By way of example, systems that are operative to automatically optically inspect printed circuit boards by comparing images of a printed circuit board under inspection to a computer generated reference that is prepared from a computer aided manufacturing file, are generally commercially available. One typical configuration of such a system includes an Xpert 1700™ computer aided manufacturing system, CDR 300™ and Ref-Manager 300™ software appliances, and an Inspire 9000™ AOI system, all available from Orbotech Ltd. of Yavne, Israel.
Patterns inspected by conventional AOI systems typically are formed from copper conductors deposited on a non-conductive substrate. The patterns inspected are binary in nature inasmuch as only two optically identifiable populations, copper conductor and substrate, are considered.
The following co-pending patent applications, which are assigned to the same assignee as the present application and which describe apparatus and methods suitable for automatically optically inspecting patterned articles, such as electrical circuits, are hereby incorporated herein by reference:
Israel Patent Application 131092, filed Jul. 25, 1999; and
Israel Patent Application 131282, filed Aug. 5, 1999.
In co-pending Israel patent applications 131092 and 131282, hardware and software parts of an automated optical inspection system operative to inspect non-binary patterns are described. Such non-binary patterns may be found, for example, on the outer layer of a finished printed circuit board, ball grid array substrate, tape automated bonding substrate, or other similar carriers and chip packaging. These non-binary patterns, in addition to an electrical circuit, include various exotic metal coatings on selected portions of the conductors and translucent solder masks that cover selected parts of the circuit.
Conventional computer generated references of binary images, such as references typically used in the inspection of electrical circuits on printed circuit boards, do not provide complete information about the location of multiple optically identifiable populations or combinations of populations. Thus, for example, in the context of automated optical inspection of the surface of a finished ball grid array substrate, which typically includes at least copper conductors deposited on a substrate, a translucent solder mask that partly covers the conductors and gold coatings on some exposed portions of the conductors, conventional binary references used in the automated optical inspection of electrical circuits do not contain information about the existence, location and integrity of gold coatings on conductors, or about the existence, location and integrity of solder mask relative to the conductors or the substrate.
Additionally, conventional computer generated references, such as references typically used in the inspection of electrical circuits on printed circuit boards, typically provide information about pixel values for individual pixels in an image and an electrical circuit to be inspected, or about the existence and location of features in the electrical circuit. Information about the existence or location of contours and edges is not provided.
Although a reference useful for inspecting a pattern comprising multiple optically identifiable populations and/or contours and edges may be prepared from the actual inspection of a perfect or “golden” pattern, the use of a reference derived from actual inspection is problematic. As readily is appreciated, the process of preparing a reference from inspection of an article believed to have a perfect pattern is time consuming and necessitates large resources such as computer memory. Moreover, a reference prepared, for example, from a computerized design file (a “CAD file”) or from a computerized manufacture file (a “CAM”) file can provide information not directly available in a reference derived from actual inspection. For example, regions external to the electric circuit that do not require inspection, vias and step and repeat data may be available in a CAD file or CAM file. Additionally, there is always uncertainty as to whether the pattern used to derive a golden reference from inspection of any article was indeed perfect.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.